The present invention pertains to micro-electromechanical systems (MEMS) devices. More particularly, the present invention relates to improvements in electrodes for use in MEMS devices.
MEMS devices have been used in a variety of optical applications. The prior art is replete with examples of MEMS-based optical modulators, add-drop filters, attenuators and routers.
Each optical MEMS device typically incorporates a xe2x80x9cmirrorxe2x80x9d that is capable of altering the path of a received optical signal or simply attenuating the signal""s intensity. The mirror, which is usually realized as a movable beam or plate, is configured to use either optical interference principles or simple reflection to provide the above-stated capabilities. In optical MEMS devices that rely on simple reflection, the movable beam typically comprises polysilicon or silicon that is coated with metal to provide a reflective surface. The movable beam is usually configured for movement via one of the two arrangements that are described below.
In a first arrangement 100 depicted in FIG. 1A (top view) and FIG. 1B (side view), movable, electrically conductive beam 102 is cantilevered over a cavity 104. Flat planar electrode 106 is disposed within cavity 104 beneath movable beam 102. In a second arrangement 200 depicted in FIG. 2A (top view) and FIG. 2B (side view), movable, electrically conductive beam 202 is suspended by supports 208A and 208B over cavity 204. Flat planar electrodes 206A and 206B are disposed in cavity 204 beneath movable beam 202.
As a potential difference is developed across movable beam 102 and electrode 106 of first arrangement 100, an electrostatic force is generated. The force bends movable beam 102 toward electrode 106. Similarly, as a potential difference is developed across movable beam 202 and either one of electrodes 206A or 206B, an electrostatic force is generated that draws the movable beam towards the actuated electrode. Supports 208A and 208B twist to allow movable beam 202 to move in such fashion. As beam 102 and beam 202 move, the path followed by an optical signal that is reflected therefrom is altered.
Both arrangement 100 and arrangement 200 suffer from a significant shortcoming. In particular, the actuation voltage necessary to achieve the required amount of mirror rotation (for sufficiently altering the path of an optical signal) is large (i.e., about 150 volts for a typical design). There is a need, therefore, to reduce the actuation voltage requirements of electrostatically-driven, MEMS-based, movable mirrors.
Some embodiments of the present invention provide an electrode that is capable of reducing the actuation voltage of MEMS-based mirrors.
An electrode in accordance with the present teachings declines in height along its length from a first end thereof to second end thereof. In one embodiment, the decline in height of the electrode along its length is regular or linear such that the electrode has a wedge-shaped profile. In another embodiment, the height of the electrode declines in discrete steps such that the electrode has a stepped profile.
In use, the electrode is disposed beneath a MEMS mirror (e.g., a beam, etc.). The first end of the electrode is disposed proximal to an axis of rotation or axis of bending of the mirror. Due to the geometry of the present electrode, the gap between the MEMS mirror and the surface of the electrode can be smaller than the gap between a MEMS mirror and the flat-planar electrodes in the prior art. Consequently, in such embodiments, the voltage requirement for a MEMS mirror that is actuated by the present electrode is reduced relative to voltage requirement for a MEMS mirror that is actuated by electrodes of the prior art.